The invention concerns generally a machine and more particularly a hydrodynamic machine involving a flow of a fluid medium, for example a pump, an agitator or the like. The invention further concerns a wheel such as an impeller or propeller, preferably for use in a hydrodynamic machine.
A typical configuration of a machine such as a hydrodynamic machine such as a pump or agitator comprises a stationary housing with a motor-driven shaft supported in the housing and a wheel on the shaft for moving a fluid medium. The shaft engages through an opening in the housing, and the wheel which is arranged at the free end of the shaft is disposed outside the housing. The hub of the wheel engages into the opening in the housing, forming an annular gap between the inside wall of the opening and the outside wall of the hub. A seal seals off the shaft and/or the hub and the housing relative to the medium and a spiral arrangement is arranged in the region of the hub in fixed relationship therewith to produce a flow of medium which is directed out of the annular gap to prevent particles from being deposited therein.
In this respect, consideration may be given to EP 0 252 037 B1 disclosing a sealing arrangement for an agitator or a pump, which, as indicated above, has in the region of the annular gap between the hub of the wheel and the opening in the housing a spiral arrangement which opposes particle deposit in the gap by virtue of producing a fluid flow which is directed out of same. In that structure the spiral arrangement is of such a configuration that a spiral surface structure is formed in the inside wall of the opening in the housing and the outside wall of the wheel of the hub. The annular gap is in the form of a cylindrical gap between those mutually oppositely disposed concentric walls which in effect are provided respectively with male and female screwthread configurations. When the hub is rotated in the opening in the housing, an outwardly directed flow is generated in the annular gap, and is intended to transport particles outwardly thereof. In addition, provided at the upper edge of the opening in the housing is a cutting device insofar as cutting edges are provided at the annular edge of the opening in the housing and on the wheel hub. When the hub rotates, the cutting edges co-operate with each other and are intended to make the particles as small as possible.
It will be appreciated that this design configuration is relatively complicated and expensive in regard to its structure as it involves machining a plurality of mutually co-operating, especially machined surfaces on each of the co-operating components. Disturbances can occur in operation thereof, particularly if there are relatively large amounts of large-size particles, for on the one hand the operation of reducing the size of the particles means that the amount of material which can involve sedimentation in the annular gap is increased, while on the other hand blockages can occur in the region of the cutting arrangement itself, particularly once a certain amount of wear of the cutting edges has occurred.
Attention may also be directed to U.S. Pat. No 6,053,500 A disclosing a further sealing arrangement for a shaft of a pump impeller. That arrangement has a housing with an opening therein, into which the hub of the impeller engages. Provided in the region of the inside wall of the opening is a screw pitch which is formed in fixed relationship with the housing and operable to counteract particle deposition there. When the hub rotates in the opening in the housing, the result is a flow therein, with which particles are to a certain extent entrained outwardly thereof.
Reference may also be made to EP 0 542 530 B1 disclosing a seal for a shaft, in which the sealing member itself has a spiral structure and thereby, upon rotation of the shaft, a flow which is directed outwardly in the region of the seal is generated. That is intended to oppose deposit of particles to a certain extent.
EP 0 879 977 A2 also involves a further sealing arrangement for a shaft, in which a sealing member comprising polymer material has sealing lips with taper angles of different gradients, which co-operate with the peripheral sealing surface on the shaft. The shaft in that region has grooves extending in a helical configuration, with a groove depth of less than 15 xcexcm, in order to transport lubricant back into the sealing region in order to lubricate the sealing edges during rotation of the shaft.
An object of the present invention is to provide a hydrodynamic machine of such a design configuration in the sealing and shaft-supporting area thereof as to counteract deposit of particles in the region of the shaft seal at the medium side in a structurally simple manner with a high level of operational reliability.
A further object of the present invention is to provide a hydrodynamic machine such as a pump or agitator adapted to resist fibrous constituents possibly contained in the medium becoming wrapped around the wheel hub.
Still another object of the invention is to provide a hydrodynamic machine which while being of a simple structure more effectively produces a flow of fluid medium operable to remove particles and other contaminating matter in the fluid medium from the region of a wheel such as an impeller or propeller of the machine.
Yet a further object of the invention is to provide a wheel such as a propeller or impeller for a hydrodynamic machine, which is capable of resisting particle deposit in its bearings and at least in part reducing the likelihood of elongate contaminating material in the fluid medium becoming wrapped around the wheel hub.
In accordance with the principles of the present invention in the machine aspect the foregoing and other objects are attained by a machine such as a hydrodynamic machine, for example a pump, agitator or the like, comprising a stationary housing with a motor-driven shaft which is supported in the housing and which has a preferably non-rotatably connected wheel for moving a fluid medium, more particularly for example an impeller, propeller or the like. The shaft extends coaxially through a pot-shaped opening in the housing and the wheel which is arranged at the free end of the shaft is disposed outside the housing. The hub of the wheel on the shaft engages into the pot-shaped opening in the housing, forming an annular gap between the inside wall of the opening in the housing and the outside wall of the hub. The machine further includes a seal for sealing off the shaft and/or the hub and the housing in relation to the fluid medium, while a spiral arrangement is disposed in the region of the hub non-rotatably with respect thereto to produce a flow of medium which in the annular gap is directed out of same, to prevent particle deposit. The outside diameter and/or the cross-section of the annular gap between the inside wall of the opening in the housing and the outside wall of the wheel hub is or are of a configuration which increases towards the wheel.
Further in accordance with the principles of the invention, in the wheel aspect thereof, the foregoing and other objects are attained by a wheel in the form of an impeller or propeller, preferably for use in a hydrodynamic machine such as a pump or agitator, comprising propeller blades or impeller vanes and a wheel hub, preferably for engagement into a pot-shaped opening in a housing such as a sealing housing of the hydrodynamic machine. The wheel hub is connected in one piece to the propeller blades or impeller vanes and has a spiral arrangement on its outside wall.
In a modified form of that wheel the spiral arrangement extends at the outside of the wheel hub from a position on the wheel hub which is remote from the propeller blades or impeller vanes, preferably from the end of the hub remote from the propeller blades or impeller vanes, to the underside of the propeller blades or impeller vanes.
As will be seen from the description hereinafter of preferred embodiments of the invention, the fact that the annular gap is of an outside diameter or cross-section which increases towards the exit therefrom means that the annular gap is of a conical configuration. That strengthens the flow produced upon rotation of the hub due to the action of the spiral arrangement, in the annular gap, in such a way as to produce a pronounced, outwardly directed preferably spiral flow of fluid medium. Due to the increasing cross-section of the annular gap, the outwardly directed flow is also strengthened and opposes the formation of blockage in the annular gap.
The spiral arrangement is formed non-rotatably with the hub, preferably in the form of raised portions or recesses extending in a spiral configuration on the outside wall of the hub. The spiral raised portions or recesses can extend around the hub in the form of interconnected continuous spirals, but alternatively they can also be formed in a region-wise manner as interrupted spiral portions. In accordance with preferred features of the invention, the spiral-shaped or screw-shaped configurations are formed directly in the outside wall of the hub, thus in effect in the form of spiral-shaped or screw-shaped surface structuring in the form of a male screwthread on the surface of the hub. The inside wall of the opening in the housing, into which that hub engages to afford the annular gap, can have an inside surface which is preferably conical or of a tapered configuration. It is possible but not necessary to forego a spiral arrangement in the region of the inside wall of the opening in the housing, such as to co-operate with the spiral arrangement on the hub, and that elimination of the spiral arrangement in the opening in the housing can afford advantages from the point of view of the manufacturing process involved. It is also possible to eliminate a cutting arrangement in the region of the annular gap for the above-discussed configurations according to the invention produce in the region of the annular gap a particularly strong and effective outwardly directed flow which ensures that even relatively large particles and in particular fibrous material are transported away.
Apart from that consideration, the deposit of particles in the annular gap is also at least substantially prevented by virtue of a particular arrangement and configuration of the seal. For that purpose, in accordance with a further preferred feature of the invention, the wheel hub can have a coaxial opening which is open at the end remote from the wheel and in which at least a part of the seal is arranged. The seal can have a sliding ring which is fixed with respect to the housing and which has a sealing surface at the housing side and which is arranged in the region of a housing aperture through which the shaft passes. As a further component part, the seal may also have a sliding ring which is non-rotatable with respect to the shaft or the hub and which is arranged within the opening of the hub. It can co-operate with an elastic sealing element having a sealing surface on the shaft side and/or the hub side and is also arranged within the opening in the hub. Although in that arrangement the annular gap between the outside wall of the hub and the inside wall of the pot-shaped opening in the housing is provided in the immediate proximity of the seal, it is arranged at a radial and/or axial spacing with respect to the seal, for the annular gap is disposed at the outside of the hub while the seal is arranged substantially within the inner coaxial opening in the hub. That configuration on the one hand therefore prevents the formation of deposits of particles due to the flow in the annular gap while on the other hand, by virtue of the seal being arranged in a protected fashion within the opening in the hub, this arrangement provides that the seal is not accessible for a deposit of particles thereat or does not have fluid medium flowing therearound. Furthermore, the particular configuration set forth above with sliding rings means that the risk of damage to the seal due to possible particle deposits and the like can be reduced. The sliding ring which is fixed with respect to the housing and/or the sliding ring which is fixed with respect to the hub or the shaft can be made from suitable material such as ceramic material, for example silicon carbide. Such a material affords particularly good sliding and sealing properties and affords a particular degree of robustness in relation to damage caused by particle deposits and blockages.
In accordance with a further preferred feature of the invention the opening in the hub can extend from the hub end remote from the wheel, along half or a third of the axial length of the hub. That affords sufficient structural space for the seal.
In another preferred feature of the invention which can afford a particularly strong flow of fluid medium in the annular gap, the spiral arrangement extends at the outside of the wheel hub from the end of the wheel hub which is remote from the wheel, as far as the underside of the wheel or into a position at a preferably small axial spacing from the underside of the wheel. It has been found desirable in terms of producing an effective flow of fluid medium in the annular gap if the spiral arrangement initially extends over the entire axial length of the outer periphery of the hub portion which engages into the pot-shaped opening of the housing and directly forms the annular gap with the inside wall of the opening in the housing. In that case, extending the spiral arrangement on the outside of the hub to the underside of the wheel can increase the effect of transporting the particles away from the region of the exit from the annular gap and can thus serve to obviate blockages in the annular gap. A particularly effective flow can be achieved if the spiral arrangement is adapted to form a transition into the working surfaces of the wheel, preferably the wheel blades or the like.
In accordance with a further preferred feature of the wheel which can be for example in the form of a propeller, the hub of the propeller, in the region where the blades are formed thereon, can involve a thickening in the outside diameter of the hub so that a transitional region is afforded between that region of the hub in which the propeller blades are arranged and the adjoining region of the hub which is remote from the propeller blades. The transitional region can be bevelled, stepped or rounded. The thickening in the outside diameter of the hub is afforded particularly in embodiments of propellers having more than two blades, for example in the case of a three-bladed propeller. It is generally possible to forego the increase in the outside diameter of the hub, when dealing with a propeller having two blades. The increase in the hub outside diameter is at least desirable and may be necessary when dealing with propellers having a plurality of blades, in order to ensure that the locations at which the propeller blades are formed on the hub, for example the roots of the blades, are at the outside periphery of the hub. Particularly for reasons related to manufacture, the thickening in the case of propellers of a relatively large diameter is of a substantially spherical configuration, while in the case of propellers of a smaller diameter the thickening can be in the form of a cylindrical portion.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments.